1. Technical Field
Embodiments of the invention relate generally to marine propulsion. Particular embodiments relate to azimuthing drives for marine propulsion.
2. Discussion of Art
Marine propulsion can be accomplished by various means. Most commonly, a marine vessel is driven forward by a shaft-mounted propulsor external to the vessel, such as an open propeller or a shrouded screw. Also known are water jet propulsors, which are essentially screws shrouded by the marine vessel itself. Such means for propulsion can be configured as azimuthing drives, which include propulsors that can be swiveled about axes perpendicular to the thrust axis of the drive, thereby redirecting the thrust force within an azimuthal plane.
Conventionally, an azimuthing drive has its propulsor driven from a vertical shaft, which in turn is driven by a vertically- or horizontally-arranged engine, e.g., a diesel engine. For example, a horizontally-arranged engine will have its crankshaft extending in a horizontal plane. The horizontally-arranged engine crankshaft will drive the vertical shaft of the azimuthing drive via a bevel gear or the like.
In operation, efficiency of the propulsion system with azimuthing drive is limited by the fuel consumption profile of the driving engine (prime mover). Typically, an engine will have a first optimum range of operating speeds and loads, whereas a propulsor will have a different optimum range of operating speeds and loads. Intervening gearing can aid in achieving a desirable combination of engine speed and propulsor speed, however, it is difficult to provide efficient gearing that enables full use of the driving engine and of the propulsor throughout both optimum speed and loading ranges.
In view of the above, it may be desirable to provide an azimuthing drive system that enables better operation and utilization of the engine during the operation of the vessel than systems currently available.